The present invention relates to pressure transducer devices and in particular to a pressure transducer device with a contact resistance which varies in response to in a pressure force.
The present invention responds to a need for a low-cost, replaceable, simple and easily fabricated pressure transducer which can be used in any one of a number of applications but which can particularly be used in conjunction with a pressure actuated musical instrument such as an electronic saxaphone. In such an instrument it is desired to provide a mouthpiece into which a musician blows to cause variations in the amount of air pressure in a chamber to alter the volume of the tone generated by an electronic circuit. Thus, as the air pressure in the chamber is increased the volume will increase and vice versa. The musician will thereby have complete control of the volume of the tone or tones generated by the electronic circuitry of the musical instrument.
In order to achieve this result, it is necessary to provide a pressure transducer device which will be responsive to changes in pressure inside the chamber to cause variations in an electrical characteristic, such as a resistance, which is interconnected in the tone generating circuit.
In addition, a musician will be blowing into the chamber to cause increases and decreases in the pressure, certain amounts of moisture will enter the chamber and come in contact with a pressure transducer disposed therein. Hence, it is desired that the pressure transducer device be constructed so that it is not affected by such moisture in the chamber.
One possible pressure transducer device may be made by providing a first contact conductor on a flexible Mylar base, a second contact conductor on a second base material and a semiconducting composition disposed on one or both of the first and second contact conductors. The two contact conductors are then aligned in transverse, electrically spaced, relationship. In operation, as the flexible Mylar base is displaced, the two contact conductors with the semiconducting composition therebetween are brought into electrical conducting relationship. As the depression pressure increases the contact resistance through the semiconducting composition will decrease thus providing a pressure resistive transducer device.
While this device is suitable in some applications, it lacks sensitivity because of the inelastic nature of the flexible Mylar base material.
One possible way of increasing the sensitivity is to dispose the conductive and semiconductive material on a resilient stretchable membrane or diaphragm which provides positive action both when pressure is increased and when pressure is decreased. Such a diaphragm material could, for example, be dam rubber. However, one problem with such a device is that the conductor must expand and contract with the diaphragm in response to changes in pressure. This could eventually cause breaks in the conductor disposed on the diaphragm resulting in the failure of the pressure transducer device.
The present invention overcomes the problem of a lack of sensitivity when Mylar alone is used and yet is not subject to the conductor breaks caused by disposing the conductor on the diaphragm. Specifically, the pressure transducer in accordance with the invention provides a diaphragm adhesively attached about its peripheral edges to a spacer which is adhesively attached about the peripheral edges of a flexible Mylar member with a conductor disposed thereon. The diaphragm is then attached at a center location directly to the center of the Mylar member. When no pressure is applied to the diaphragm, the diaphragm positively pulls the flexible Mylar base away from a second base member because of its elastic characteristics. When a pressure is exerted against the diaphragm, the conductor on the flexible Mylar is forced into electrical conducting relationship with a second conductor on the second base member. The diaphragm thus imparts the positive action to the flexible Mylar. The flexible Mylar moves in response to the movement of the diaphragm.
In such an arrangement, it has been found that the sensitivity of the pressure transducer device in accordance with the invention is increased because of the aforedescribed positive movement of the diaphragm. Thus, the stretchable resilient characteristic of the diaphragm is imparted to the Mylar which does not have the desired resilient stretchable characteristics but which does provide a nonstretchable support member upon which the contact conductors can be disposed.